This application claims priority to an application entitled xe2x80x9cPower Control Device and Method for Mobile Communication Systemxe2x80x9d filed in the Korean Industrial Property Office on Jun. 17, 1999 and assigned Ser. No. 99-22791, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to a mobile communication system, and, in particular, to a power control device and method for improving the quality of calls between mobile stations in a CDMA (Code Division Multiple Access) mobile communication system.
2. Description of the Related Art
In a typical CDMA system, for a call between a mobile station and a telephone connected by wire to an existing wire telephone network, the mobile station exchanges a signal with a base station and the base station exchanges a signal with the existing wire telephone network. Since the base station is connected to the existing wire telephone network by wire, the error rate of the signals transmitted between the base station and the existing wire telephone network is very low. Therefore, the overall call quality between the mobile station and the existing wire telephone depends on the condition of the channel between the mobile station and the base station.
On the other hand, for a call between mobile stations, the signal is transmitted through three links: a first link between the first mobile station and a first base station, a second link between the first base station and a second base station, and a third link between the second base station and the second mobile station. In this case, unlike the call between the mobile station and the telephone on the existing wire telephone network, there are two call connections maintained between a mobile station and a base station, causing degradation of the overall call quality.
FIG. 1A shows how to connect a call between a mobile station and a wire telephone using a general power control method, and FIG. 1B shows how to connect a call between mobile stations using the general power control method. Referring to FIGS. 1A and 1B, a frame error rate (FER) for a power control frame provided between the mobile station and the base station is conventionally set to a fixed value. The FER is a typical index indicating the call quality of the mobile communication system.
For example, for a call between a mobile station and a wired telephone, if it is assumed that the call quality between mobile station 101 and base station 102 is fixed to x% FER and a call quality between the base station 102 and a wired telephone 103, connected to each other by wire, is zero FER (i.e., no error), then the call quality between the mobile station 101 and the wire telephone 103 is x% FER in FIG. 1A. However, in FIG. 1B, the call quality between mobile station 104 and mobile station 107 becomes 2x% FER, since the call quality between mobile station 104 and base station 105 is x% FER and the call quality between base station 106 and mobile station 107 is also x% FER. Like the wired connection in FIG. 1A, the wired connection between base station 105 and base station 106 has zero FER.
That is, conventionally, power control has been performed using the same target FER regardless of whether the call is between mobile stations or between a mobile station and a wired telephone. Therefore, in a conventional mobile communication system which mainly transmits and receives the voice signals, the call quality is degraded during a call between mobile stations. Furthermore, in a 3rd generation mobile communication system which also exchanges image signals, data signals and packet signals, the degradation of call quality on a call between mobile stations will reduce the communication reliability of the image signals and the data signals. In particular, when packet signals are exchanged between the mobile stations, the frequency of retransmission increases undesirably.
It is, therefore, an object of the present invention to provide a power control device and method for maintaining equivalent or greater call quality for calls between mobile stations as calls between a mobile station and a wired telephone.
It is another object of the present invention to provide a power control device and method for performing different power control according to the type of mobile station in service.
It is further another object of the present invention to provide a power control device and method in which a mobile station performs power control according to a power control parameter corresponding to a call type provided from a base station.
It is yet another object of the present invention to provide a power control device and method in which a mobile station performs power control by reading a power control parameter value corresponding to call type information provided from a base station.
It is still another object of the present invention to provide a power control device and method for performing power control using a different power control parameter value depending on whether there is a normal call request or a high-quality call request by a user of the mobile station.
In accordance with one embodiment of the present invention, there is provided a power control device and method in a mobile communication system. Upon receipt of a call request, a base station selects a call type corresponding to the call request. The base station has a memory for storing power control parameter values for every call type serviceable in the mobile communication system. The base station reads a power control parameter value corresponding to the selected call type from the memory, and provides the read power control parameter value to the mobile station to perform outer loop power control.
In accordance with another embodiment of the present invention, there is provided a power control device and method in a mobile communication system. A mobile station receives a call type from a base station. The mobile station has a memory for storing power control parameter values for every call type serviceable in the mobile communication system. The mobile station reads a power control parameter value corresponding to the received call type from the memory, and performs outer loop power control according to the read power control parameter value.
In accordance with further another embodiment of the present invention, there is provided a power control device and method in a mobile communication system. Upon receipt of a call request from a mobile station, a base station selects a call type corresponding to the call request. The base station has a memory for storing power control parameter values according to call quality and every call type serviceable in the mobile communication system. The base station sets the call quality at a request of the mobile station. Thereafter, the base station reads a power control parameter value corresponding to the selected call type and the set call quality from the memory, and provides the read power control parameter value to the mobile station to perform outer loop power control.